Radio receiver



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G. W. FYLER RADIO RECEIVER Den. 2%,, W49

Filed May 17, 1943 HPPA RA TUS 00/24. 816M41- AMPL [FYI/VG c HA lV/VEL S/GIVAL REPRODUCl/VG APP 7,944 TUS Invemcor". George \Mwyleb, b J M, M

y His A'k'borney.

Patented Dec. 20, 1949 RADIO RECEIVER George W. Fyler, Stratford, Conn, assignor to General Electric Company, a corporation of New York Application May 17, 1943, Serial No. 487,249

9 Claims.

My invention relates to radio receivers, and more particularly to receivers capable of receiving both frequency and amplitude modulated carrier waves. This application is a continuation-inpart of my copending application, Serial No. 453,821, filed August 6, 1942, and assigned to the same assignee as the instant application.

The invention has for one of its objects the provision of a radio receiver which may be produced at reduced cost and is capable of the different types of radio reception now common in household reception.

At the present time the difierent signals commonly radiated for home reception include television signals comprising a carrier wave modulated in accordance with the transmitted picture image and a carrier wave modulated, usually with respect to frequency, in accordance with the sound to accompany the picture reproduction. Signals comprising programs of music or speech are also commonly transmitted by frequency modulation of very high frequency or short waves and by amplitude modulation of longer waves of relatively low frequency.

It is a principal object of my invention to provide a combined radio receiver capable of either frequency modulation or amplitude modulation reception.

It is a further object of my invention to provide a new and improved combined demodulating circuit for frequency modulation and amplitude modulation reception.

One specific object of my invention is the provision of a combined frequency modulation and amplitude modulation detection circuit which shall function to demodulate either a frequency or amplitude modulated carrier Wave without requiring any circuit switching, particularly at the detector load.

It is another object of my invention to provide a combined amplitude modulation and frequency modulation radio receiving apparatus which shall have a single automatic volume control lead operable during either type of signal reception.

In carrying out my invention, I provide combined frequency modulation and amplitude modulation detector circuits including a load resistor common to both circuits and arranged to derive signal voltages at a common point for either type of reception. I also provide a pair of unilaterally conducting rectifier circuits associated with separate frequency and amplitude modulation channels, respectively, and including a common load resistorfor developing an automatic volume control bias voltage for either type of reception.

The novel features which I believe to be characteristlc of my invention are set forth with particularity in the appended claims. My invention itself, however, both as to the organization and the method of operation together with further objects and advantages thereof may best be understood by reference to the following detailed description taken in conjunction with the accompanying drawings, in which Fig. 1 is a schematic circuit diagram of a radio receiving apparatus embodying my invention in one form, and Fig. 2 is a schematic circuit diagram of a. radio receiver embodying my invention in another form.

Referring now to the drawings, and particularly to Fig. 1, I have shown by way of illustration a radio receiving apparatus of the superheterodyne type comprising an antenna I0 and a multiple wave band signalchannel ll terminating in an intermediate frequency amplifier l2. The portion II of the signal channel is shown only in block form and suitably comprises one or more radio frequency amplifiers, an adjustable local oscillator, aconverter or mixer for deriving from the radio frequency signal wave a signal modulated wave of predetermined intermediate frequency, and a plurality of stages of intermediated frequency amplification preceding the amplifier l2. The output of the portion H of the signal channel is impressed between a cathode l3 and a control grid 14 of the intermediate frequency amplifier l2. The amplifier l2 also includes an anode l5 connected through the primary windings l6 and I! of a pair of intermediate frequency transformers l8 and is respectively in series circuit relation to the positive terminal B+ of a suitable sourceof unidirectional current supply such as a battery (not shown). The cathode l3 of the amplifier I 2 is grounded and connected to the negative terminal of the battery. Commonly the intermediate frequency amplifier I2 also includes a screen grid 29 and a suppressor grid 2| connected, respectively, to the terminal 3+ and to the oathode [3.

At the present time it is customary to operate the intermediate frequency channel of a)! frequency modulation superheterodyne receiver at a frequency of perhaps 8 or 12 megacycles per second. By way of illustration, the intermediate frequencyof 8.25 megacycles (mc.) commonly used in television receivers has been chosen for the frequency modulation signal channel and the transformer I8 is indicated as tuned to this frequency by suitable primary and secondary tuning condensers 22 and 23 respectively. Similarly, an intermediate frequency of 455 kilocycles per second is common for the intermediate frequency channel of an amplitude modulation superheterodyne receiver. As indicated on the drawing, the transformer [9 will be assumed to be tuned to 455 kilocycles (kc.) by means of suitable primary and secondary tuning condensers 24 and 25, respectively. It will, of course, be understood by those skilled in the art, particularly in View of the following description, that my invention is not in any sense limited to a superheterodyne receiver, but that, if desired the heterodyning stage may be omitted and the signal channel arranged to transmit signal waves within high and low bands of frequencies for frequency and amplitude modulation reception, respectively.

. The portion ll of the signal channel preceding the amplifier I2 is suitably provided with one series of amplification stages tuned to the high intermediate frequency of 8.25 me. for frequency modulation reception and a. second series of am plification stages tuned to 455 kc. for amplitude modulation reception. The dual signal channel II includes a two-position selector switch Ha arranged to disable the unused portion of the signal channel when either the high or low frequency stages are in use. The switch Ila precedes the amplification stages so that switching is accomplished at low signal levels, thereby to prevent transmission of undesired signals to the discriminator. Heretofore, in combined frequency modulation and amplitude modulation receivers, switching has been carried out at the discriminator load by providing a switch for selectably connecting at least one of the discriminator diodes in a frequency discriminating circuit or in an amplitude detection circuit. By switching at low signal levels, the dual detector circuits may be permanently connected in a manner hereinafter to be described. This arrangement is preferable to detector load switching because it prevents amplification and transmission of the undesired signal to the detector level. It has been found that at high signal levels the small capacity of a switch and its necessary connecting leads is sufficient to produce objectionable coupling and hum.

The transformer 48 includes a secondary winding 25 connected to supply to the input of an amplitude limiting electric discharge device 21 the high intermediate frequency waves signal modulated in frequency. The electric discharge tube 2'! comprises a cathode 28, an anode 29, a control grid 30, a screen grid 3| and a suppressor grid 32. The secondary winding 26 of the transformer I8 is connected between the cathode 28 and the control grid 30 of the tube 21 through a direct current blocking capacitor 38. The screen grid 3i and the suppressor grid 32 are connected conventionally to the positive terminal of asource of unidirectional current supply and to the oathode 28, respectively. The output circuit for the limiter tube 21 comprises a primary winding 33 of a discriminator input transformer 34 connected between the anode 29 and the positive terminal B+ of a suitable source of unidirectional current supply such as a battery (not shown).

The output circuit is completed by a switch 35 arranged to connect the cathode 28 to ground at 35, the negative terminal of the battery being also grounded. The battery is bypassed for high fre- 4 quency currents by a capacitor 31. It will be understood by those skilled in the art that the amplitude of a signal wave appearing in the output circuit of the device 2'! is limited by saturation to a predetermined maximum value.

A frequency discriminating circuit 39 is connected to the secondary winding 40 of the transformer 34. The discriminator 39, shown by way of illustration, is of a well known type and cornprises a pair of diode rectifiers 42 and 43 having their anodes 44 and 45, respectively, connected to opposite terminals of the secondary winding 40 of the transformer 34 and their cathodes 46 and 4?, respectively, connected to the opposite terminals of a discriminator load resistor t I. The cathode 41 is grounded at 48. The midpoint of the load resistor 4! is connected through a connection common to the two rectifier circuits to the midpoint of the transformer secondary Winding 40. The primary and secondary windings 33 and 40 of the transformer 34 are tuned to the high intermediate frequency, assumed to be 8.25 mega cycles by means of shunt capacitors 49 and 50, respectively. The voltage of the highpotential terminal of the transformer primary winding 33 is impressed upon the midpoint of the transform er secondary winding 40 through a coupling capacitor 5i.

A discriminator of the above type is claimed and its mode ofoperation is described in detail in Patent 2.121103 issued to S. W. Seeley on June 21, I938. The operation maybe explained briefly as follows. By reason of the coupling through the. capacitor 5| and the tuning of the primary and secondary windings of the transformer 34 the high frequency electromotive forces across the upper and lower halves of the transformer winding 40 vary oppositely in instantaneous magnitude in accordance with instantaneous signal deviations in frequency of the received carrier wave from its mean frequency. Accordingly, the instantaneous voltage drops across the upper and lower halves of the load resistor 4| vary oppositely in response to such frequency deviations, so that the net voltage between opposite terminals of the resistor 4| varies in instantaneous magnitude in accordance with signal modulation of the frequency modulated wave. The signal voltage between the terminals of the discriminator load resistor 4] is supplied through a suitable low pass filter 52, 53, 54 and a direct current blocking capacitor 55 to an output circuit comprising a volume control potentiometer 56. From the potentiometer 56 the signal voltage is supplied to a suitable signal reproducing apparatus 51, which preferably comprises one or more audio amplifier stages and a signal reproducing device such as a loudspeaker, headphone or the like.

An amplitude modulation detector-comprising a series diode rectifier circuit is connected to the tuned secondary winding 58 of the 4-55 kc. transformer I 9. This circuit includes a unilateral discharge device 59 having an anode connected to one terminal of the secondary Winding as and a cathode Bl permanently connected through the filter resistor 54 and the discriminator load resistor 4! to ground. The cathode 6! of the diode 59 is also bypassed to ground for intermediate frequencies by a capacitor 62. The other terminal of the secondary winding 58 is connected to ground through a load resistor 63 of high resist ance which is bypassed for high frequency alter-'- nating currents by a suitable capacitor 64.

For automatic volume control of the signal channel II a single automatic volume. control lead 65 is connected to the low potential terminal of the secondary winding 26 of the limiter input transformer l8 and through a current limiting resistor 66 to the negative terminal of the resistor 53 in the circuit of the diode detector 59. As will be more fully explained hereinafter, there is impressed upon the lead 65 a negative bias potential proportional to the magnitude of a received carrier wave, Whether of high or low intermediate frequency. It will be understood that the lead 65 is connected to control the amplification of the signal channel H in any well known manner, as by impressing a negative biasing potential on the control electrodes of the discharge amplifiers employed therein, and therefore serves to maintain substantially constant the carrier magnitude and signal volume upon the reception of either frequency modulated or amplitude modulated waves.

In view of the foregoing detailed description of the circuit arrangement of the receiver illustrated in Fig. 1, the mode of operation of the receiver will be understood from the following description.

Let it first be assumed that it is desired to receive a frequency modulated signal wave. To prepare for such operation the local oscillator in the signal channel H is first adjusted to provide a beat frequency of 8.25 megacycles. The selector switch I la is then positioned to complete connection of the frequency modulation channel and to disable the amplitude modulation channel and the limiter ground switch 35 is closed. The intermediate frequency wave is now amplified and appears in the output circuit of the intermediate frequency amplifier 12. Since this output circuit comprises a pair of serially connected tuned circuits I5, 22 and H, 2 3, and since only the circuit I6, 22 is tuned for resonance at the high intermediate frequency of 8.25 mc., substantially the entire output voltage will appear across the transformer I8. For the high intermediate frequency the transformer winding ll provides substantially no impedance, since this winding is tuned for resonance at the low intermediate frequency of 455 kc. Accordingly, the input voltage to the amplitude modulation diode detector 59 is substantially zero. Thus, the amplitude detection circuit, though permanently connected to include the discriminator load resistor ll, receives substantially no energization during frequency modulation reception. Closure of the limiter ground switch 35 completes the output circuit for the limiter tube 21 through the discriminator transformer 34, so that signal waves are transmitted through the limiter and signal voltages are supplied to the volume control potentiometer 55 in a manner well understood by those skilled in the art.

When the ground switch 35 is closed for the reception of frequency modulated waves, it completes not only the limiter output circuit through the transformer winding 33, but also completes a direct current circuit across the blocking capacitor 38 through the load resistor 63. This circuit may be followed from the high potential terminal of the secondary winding 26 of the transformer !8 through control grid 35 and cathode 26, ground switch 35, and resistors 63 and 66 to the low potential terminal of the transformer winding 26. Through this circuit grid rectification of the received frequency modulated carrier wave takes place, thereby to provide across the resistors 63 and 66 a unidirectional bias potential proportional to the magnitude of the high intermediate frequency carrier wave. This unidirectional po-'- tential is supplied from the negative terminal of the resistor 66 and through the automatic volume control lead 65 to the signal channel II where it is applied to control the amplification in such a manner as to maintain substantially constant the magnitude of the frequency modulated carrier wave.

If now it is desired to receive an amplitude modulated wave, the local oscillator in the signal channel II is adjusted to provide an intermediate frequency of 455 kc. The selector switch Ila is positioned to connect the L55 kc. intermediate frequency channel and to disable the 8.25 mo. intermediate frequency channel. The ground switch 35 is also opened to disable the high intermediate frequency channel through the limiter tube 21. Since the diode detector circuit through the discharge device 59 is permanently connected and includes the common discriminator and detector load resistor 4|, no switching operation is necessary to complete the detector circuit and the signal voltage will appear at the same point as in frequency modulation reception. When a 455 kc. wave is received in the output circuit of the intermediate frequency amplifier l2, substantially the entire voltage at low intermediate frequency appears across the primary winding [1 of the transformer I9, the winding l6 of the transformer l3 providing substantially zero impedance at this frequency. An amplitude modulated carrier wave of 455 kc. is therefore supplied to the diode detector circuit including the discharge device 59 and the diod load resistor dl. The signal wave is demodulated in this rectifier circuit in a manner well understood by those skilled in the art and provides across the resistor M a signal voltage which is supplied through the filter 52, 53, 54 and the blocking capacitor 55 to the volume control potentiometer 56. It will be recalled that the series diode detector circuit through the discharge device 59 also includes the load resistor 63. The negative terminal of this resistor is connected, through the resistor 56 and the volume control lead 55, to the signal channel ll. Thus, the lead 65 now supplies to the signal channel II a unidirectional bias potential proportional to the magnitude of the received carrier wave of low intermediate frequency for maintaining substantially constant the carrier wave magnitude.

The reason for the inclusion of the limiter ground switch 35 is now evident. By reason of the series connection of the primary windings l6 and ll of the transformers l8 and IS in the output circuit of the amplifier l2, the 455 kc. signal wave transmitted to the transformed H9 in amplitude modulation reception apears also across the transformer 18. While very little 455 kc. voltage appears across the transformer 18, the slight voltage present may give rise to some noise if impressed upon the detector circuits. To preclude such noise, the transmission channel through the limiter 21 is preferably, though not necessarily, disabled by the ground switch for amplitude modulation reception.

At Fig. 2 I have shown another combined frequency modulation and amplitude modulation radio receiving apparatus which in certain conventional aspects is similar to the receiver of Fig. l, but which embodies :my invention in another form. The principal feature of the arrangement of Fig. 2 is that the permanently connected diode detector circuit for amplitude modulation detection utilizes one of the frequency modulation discriminator diodes as an amplitude modulation detector, thereby eliminating the diode 59 of Fig. 1. At Fig. 2 many parts of the apparatus are similar to those illustrated in connection with Fig. 1, and corresponding parts have been assigned like reference numerals.

Referring now to Fig. 2, it will be observed that the high intermediate frequency channel for fre-' quency modulated waves, including the limiter 21, is substantially the same as that illustrated at Fig. 1. The discriminator circuit 39 is slightly modified with respect to Fig. l in that the rectifier circuit through the lower discriminator diode 43 includes the secondary winding 58 of the tuned low frequency transformer IS. The winding 58 is interposed in the discriminator circuit between the cathode 41 of the diode 33 and the grounded terminal of the discriminator load resistor 4| However, in operation upon frequency modulation reception the discriminator circuit 39 functions in substantially the same manner as that shown at Fig. 1, since the secondary winding 58 of the transformer I9, being tuned to 455 kc, offers substantially zero impedance to the signal frequency voltages passed therethrough by the diode 41 in discriminator operation.

At Fig. 2 the permanently connected series diode rectifier circuit for signal detection of amplitude modulated waves includes not only a portion of the common discriminator and diode detectorv load resistor 4|, but includes also the discriminator diode 43 itself as an amplitude modu lation detection device. This detector circuit may be traced from the high potential terminal of the low frequency input transformer l9, through the diode 43, the lower half of the secondary Winding 40 of the discriminator input transformer 34, and the lower half of the discriminator load resistor 4| to ground and the low potential terminal of the secondary winding 58 of the transformer 9.

In operation, the receiver of Fig. 2 is prepared for frequency modulation reception by adjustment of the local oscillator to provide an intermediate frequency wave of 8.25 megacycles, selecting the 8.25 mc. portion of the channel I I by means of the switch Ila, and closing of the limiter ground switch 35. The device of Fig. 2 now functions to detect frequency modulation of a carrier wave of high intermediate frequency in substantially the same manner as described in connection with Fig. l by reason of the fact that the transformer winding 58 between the cathode 4i and the lower terminal of the discriminator load resistor 4i offers substantially no impedance to signal frequency voltages.

If now it is desired to receive amplitude modulated signal waves through the receiver of Fig. '2, the limiter ground switch is opened, the selector switch I la positioned for amplitude modulation reception, and the signal channel adjusted to provide intermediate frequency waves at 655 kc. Under these conditions, no substantial voltage at intermediate frequency appears across the secondary winding of the discriminator input transformer 34 by reason of the tuning of the limiter input transformer l8 for resonance at 8.25 megacycles and also by reason of the disabling of thelimiter output circuit at the switch 35. The limiter and discriminator are, therefore, inoperative, and only the diode detector circuit connected to the transformer I9 is supplying energy to the load resistor 4|. It will be understood that while this diode detector circuit includes the lower half of the transformer winding 40, this winding offers substantially no impedance to the signal frequency voltages appearing in the diode rectifier circuit. The transformer 34 is tuned to parallel resonance at 8,25 megacycles and its impedance for very low frequencies is negligible.

In the arrangement of Fig. 2' I also provide a single automatic volume control lead 65 operable during both frequency modulation and amplitude modulation reception. For amplitude modulation reception the lead 65 is connected through a decoupling resistor 10, a. low pass filter 7|, 72, 13 and the upper half of the discriminator load resistor 4| to the negative terminal of the diode detector load resistor, which in this case is constituted by the lower half of the resistor 4|. The low pass filter comprises a pair of serially-connected resistors H and 12 and a bypass condenser 73.

During frequency modulation reception, an automatic volume control bias is derived from a grid-cathode rectifier including the control grid 3i! and the cathode 2B of the limiter discharge device 21. This grid-cathode rectification circuit may be traced from the lower terminal of the secondary winding 26 of the limiter input transformer l8 through the control grid 30 and cathode 23 of device 2?, switch 35, ground, discriminator load resistor 4! and the filter resistors 12 and H to the lower terminal of the transformer winding 26. The negative terminal of the resistor H is connected through the decoupling resistor 10 to the automatic volume control lead 65, so that this lead provides volume control during frequency modulation reception, as well as during amplitude modulation reception. It will be noted that the lower half of the discriminator load resistor 4| is common to the automatic volume control rectifier circuits for both types of reception.

From the foregoing description it will now be evident that I have provided a combined frequency modulation and amplitude modulation detector circuit which is so arranged that no switching of the detector load is necessary in transferring between frequency modulation and amplitude modulation reception. This desirable result is attained by permanent connection of the diode detector circuit to a load circuit including at least a portion of the discriminator load resistor thereby to provide signal voltages at a common point for both frequency and amplitude modulation reception. To prevent amplification of undesired signals, a single switch may be provided preceding the amplifier stages to disable the unused signal channel at low signal level. Since the last intermediate frequency amplifier includes load impedances tuned to both high and low intermediate frequencies, it is preferable to disable during amplitude modulation reception also that portion of the frequency modulation channel following the last intermediate frequency amplifier. In this Way noise voltages, which may otherwise be transmitted through the limiter, are not impressed upon the discriminator. I provide for such disabling of the frequency modulation channel by arranging the ground switch 35 so that it disconnects at once both the limiter output circuit and the limiter grid rectification circuit through which automatic volume control is provided during frequeney modulation reception. My invention thus minimizes switching at high signal levels, and entirely avoids switching at the detector load, where even the capacity of a switch and its leads may produce undesired coupling. My invention is further characterized by the provision r of a-single automatic volume control lead which serves to provide a suitable volume control bias potential for either frequency modulation or amplitudemodulation reception. Such a single lead is rendered possible by deriving the automatic claimsto cover all such modifications as fall within the true spirit and scope of my inven- 2 tion.

, What I claim as new and desire to secure by Letters Patent of the United States is:

1. In combination, a load resistor, a pair of Tunilateral conducting devices connected between an internal point and opposite terminals respectively of said resistor, said devices being poled to pass current in opposite directions through said resistor, means for supplying a frequency modulated Wave of high frequency to be detected across each of said devices, said means including means for varying the high frequency electromotive force on said devices oppositely in response to frequency modulation of said high frequency wave, a third unilaterally conducting device per- -manently connected across at least a portion of said resistor, means for supplying an amplitude modulated wave of low frequency to be detected across said third device, and means for disabling said high frequency wave supply means without disabling said low frequency wave supply means.

2. In a receiving apparatus for electric oscillations, means for selectably supplying eitherhigh frequency Waves signal modulated infrequency or low frequency Waves signal modulated in amplitude, a pair of series connected resonant circuits coupled to said wave supply means and tuned to said high and low frequencies respectively, a load resistor, a pair of unilateral conducting devices connected between an internal point and opposite terminals respectively of said load resistor, said devices being poled to pass current in opposite directions through said re sister, means inductively coupled With said high frequency tuned circuit for limiting the. amplitude of said frequency modulated Waves and for supplying said waves to be detected across each of said devices, said means including means for varying t ie high frequency electromotive force on said devices oppositely in response to frequency modulation of said high frequency waves, means inductively coupled to said low frequency tuned circuit and permanently connected in series circuit relation with one of said devices and the associated portion of said load resistor for supplying to said one device amplitude modulated Waves of said low frequency to be detected across said portion of said resistor, and switching means for rendering said limiting means incapable of transmitting oscillations without interfering with the energization of said low frequency tuned circuit.

3. In a receiving apparatus for electric oscillations, means for selectably supplying either high frequency waves signal modulated in frequency or low frequency waves signal modulated in amplitude, a load resistor, a pair of unilateral conducting devices connected between an internal point and opposite terminals respectively of said resistor, said devices being poled to pass current in opposite directions through said resistor, a high frequency wave channel inductively associated with said wave supply means for transmitting frequency modulated waves tb be detected across each of said devices, said high frequency channel including means for varying the high frequency electromotive force on said devices oppositely in response to frequency modulation of said high frequency waves, a third unilateral conducting device permanently connected in, series circuit relation with at least a portion of said resistor, a tuned circuit inductively coupled to said wave supply means for supplying amplitude modudated waves to be detected. across said third device, and means for disabling said high frequency wave channel without interfering with the energization of said low frequency tuned circuit.

4. In a receiving apparatus for electric oscillations, means for selectably supplying either high frequency waves signal modulated in frequency or low frequency Waves signal modulated in amplitude, a load resistor, a pair of unilateral conducting devices connected between an internal point and opposite terminals respectively of said resistor, said devices being poled to pass current in opposite directions through said resistor, a pair of series connected resonant circuits coupled to said wave supply means and tuned to said high and low frequencies respectively, amplitude limiting means inductively coupled to said high frequency tuned circuit and having an out put circuit for supplying a frequency modulated wave to be detected across each of said. unilateral conducting devices, said output circuit being arranged to vary the high frequency electromotive force on said devices oppositely in response to frequency modulation of said high frequency wave, a third unilateral conducting device, means inductively coupled to said low frequency tuned circuit and permanently connected in series circuit relation with said third unilateral conducting device across at least a. portion of said resistor thereby to detect said amplitude modulated waves across said third device, and means for disabling said output circuit of said amplitude limiter without interfering with the energization of said low frequency tuned circuit.

5. In a receiver for electric oscillations, a signal channel arranged selectably to transmit either high frequency carrier waves signal modulated in frequency or low frequency carrier waves signal modulated in amplitude, a load resistor, a pair of rectifier circuits each including a separate unilateral conducting device and a common portion of said load resistor, a pair of resonant circuits tuned to said low and high frequencies respectively, each of said resonant circuits being inductively coupled to said signal channel and connected to supply to one of said rectifier circuits a carrier wave at the resonant frequency thereof, means for selectably utilizing the unidirectional bias potentials developed across said common portion of said load resistor to control said signal channel and to maintain substantially constant the amplitude of received carrier Waves of either low or high frequency, and means for disabling one of said rectifier circuits when the other of said circuits is energized.

6. In a receiver for electric oscillations, a signal channel arranged selectably to transmit either high frequency carrier waves signal modulated in frequency or low frequency carrier waves signal modulated in amplitude, frequency responsive means for demodulating said high frequency carrier waves, a grid-controlled electric discharge device connecting said frequency responsive means and said signal channel for limiting the amplitude of said high frequency carrier waves, means including a load resistor connected in circuit between the grid and cathode of said discharge device for rectifying said high frequency waves, means coupled to said signal channel and including at least a portion of said load resistor for demodulating said low frequency carrier waves, means for disabling said grid-cathode circuit when said low frequency waves are received, and means for utilizing unidirectional bias potentials developed across the common portion of said load resistor to control said signal channel during both amplitude modulation and frequency modulation reception.

7 In a receiver for electric oscillations, a signal channel for selectably supplying either high frequency carrier waves signal modulated in frequency or low frequency carrier Waves signal modulated in amplitude, frequency responsive means for demodulating said high frequency waves, a grid-controlled electric discharge device connecting said frequency responsive means and said signal channel for limiting the amplitude of said high frequency waves, said signal channel including a source of high frequency wave supply interposed between the grid and cathode of said electric .discharge device, means for completing a direct current circuit between said grid and Pathode including said source of high frequency wave supply and a load resistor, means inductively coupled to said signal channel and including at least a portion of said load resistor for demodulating said low frequency waves, and means for deriving from said resistor unidirectional bias potentials for controlling the amplitude of either low or high frequency carrier waves traversing said signal channel.

8. In a receiver for electric oscillations, signal channel means for selectably supplying either a high frequency wave signal modulated in frequency or a low frequency carrier wave signal modulated in amplitude, means including a grid controlled electric discharge device coupled to said signal channel means for limiting the amplitude of said frequency modulated wave of high frequency, switching means for completing through said discharge device a grid-cathode circuit including a load resistor, said grid-cathode circuit providing across said resistor a unidirectional potential proportional to the amplitude of said high frequency carrier wave, means including a unilateral conducting device coupled to said signal channel means and connected across at :12 least a portion of said load resistor for rectifying said low frequency wave, said load resistor providing a unidirectional bias potential proportional to the amplitude of said low frequency carrier wave, and means connected between said load resistor and a portion of said signal channel for impressing one or the other of said bias potentials upon said signal channel to control the amplitude of a received carrier wave of low or high frequency.

9. In a receiver for electric oscillations, means for selectably supplying either high frequency carrier waves signal modulated in frequency or low frequency carrier waves signal modulated in amplitude, frequency responsive means inductively coupled to said wave supply means and including a load resistor for dcmodulating said high frequency waves, a grid-controlled electric discharge device interposed between said frequency responsive means and said high frequency wave supply means for limiting the amplitude of said high frequency waves, said high frequency Wave supply means being connected between the grid and cathode of said discharge device, means for completing a rectifier circuit between said grid and cathode and including said high frequency wave supply means and a second load resistor, means inductively coupled with said signal channel and permanently connected to include at least a portion of both said load resistors for demodulating said low frequency waves, and means for deriving .at least partially from common portions of said load resistors unidirectional bias potentials for selectably controlling the amplitude of low or high frequency carrier waves.

GEORGE W. FYLER.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,135,560 Carlson Nov. 8, 1938 2,163,167 Weagant June 20, 1939 2,250,862 Farrington July 29, 1941 2,256,077 Crosby Sept. 16, 1941 2,258,599 Carlson Oct. 14, 1941 2,273,098 Foster Feb. 17, 1942 2,273,134 Mountjoy Feb. 17, 1942 2,296,090 Crosby Sept. 15, 1942 2,354,959 McCoy Aug. 1, 1944 OTHER REFERENCES Radio and Television Retailing, July 19% 1, pages 42 and 43. (Copy in Scientific Library.) 

